This invention relates generally to tire treads and more specifically relates to tire treads in which the lengths of repeated design cycles or pitches are randomly modulated in certain selected sequences in order to reduce the amount of noise generated by the tire tread when the tire rolls on a road surface.
It is well known that periodic placement of tread elements (called xe2x80x9cpitchesxe2x80x9d) causes the tire to produce annoying tonal sounds during motion when rolling on a surface and that randomly modulating the placement of different lengths of pitches breaks up the tonality of such generated sound by spreading the acoustic energy more evenly throughout the noise spectrum. xe2x80x9cPitch lengthxe2x80x9d is a measure of the length from the leading edge of one base pitch to the leading edge of the next adjacent pitch in the circumferential direction of the tire. Such random modulation is referred to as xe2x80x9cpitch sequencingxe2x80x9d and is described in the publication xe2x80x9cQuieting Noise Mathematicallyxe2x80x94Its Application to Snow Tiresxe2x80x9d, S.A.E. Paper #690520, May 1969 by John H Varterasian.
Considerable investigation has been done in the past on various different techniques for arriving at many different ways of varying the pitch sequences of tire treads with the objective being noise reduction in a tire when rolling on a surface.
There are many patents which show and describe various pitch sequences and different techniques for selecting such pitch sequences. Typical examples of such patents are Lippman et al U.S. Pat. No. 2,878,852, Vorih, U.S. Pat. No. 3,926,238 and Landers, U.S. Pat. No. 4,474,223 which are briefly summarized in Williams U.S. Pat. No. 5,314,551. Examples of some later issued patents in this general field are Collette et al U.S. Pat. No. 4,721,141, Killian, U.S. Pat. No. 5,269,357, and Brown, Jr, U.S. Pat. No. 5,690,760.
The present invention provides an even further variation of pitch sequencing which can offer effective noise reduction in tire treads of various tread designs.
The present invention is directed to a tire having a tread with a plurality of load supporting elements, placed around at least one circumferential band portion of the tire, any such band portion having a plurality of pitches of three different lengths which define a preselected pitch sequence extending at least partially around the circumference of the tire, said pitches comprising a group having a largest number of medium length (M) pitches, a group having a smallest number of shortest length (S) pitches and a group having a medium number of longest length (L) pitches, the number of the M pitches being equal to the total number of S pitches plus the total number of L pitches, a segment of the circumferential section having one continuous sequence of LMSMSL pitches and the remainder of pitches in the circumferential section may be varied in at least 100 different sequences.
These and other advantages and features of the invention will hereafter appear for purposes of illustration, but not of limitation, in connection with the accompanying drawings, in which:
FIG. 1 is a perspective view of a tire having a tread pattern embodying the present invention;
FIG. 2 is an enlarged plan view of a portion of the tread of the tire illustrated in FIG. 1;
FIG. 3 is an enlarged plan view of a portion of a tread similar to that shown in FIG. 2 but having the tread patterns of the left and right half of the tread offset circumferentially from each other;
FIG. 4 is a graphical illustration of the Harmonic Analysis of the Impulse Function for a tire tread having all the pitch lengths identical around the entire circumference of the tire; and
FIG. 5 is a graphical illustration of the Harmonic Analysis of the Impulse Function for a tire tread having three pitch lengths made in accordance with the present invention.